1. Field of the Invention
The present invention relates to a projection aligner for use in a large-scale integrated circuit (LSI) manufacturing process. Moreover, the present invention relates to an aberration estimating (or evaluating) mask pattern for estimating aberration included in an optical system of a projection aligner, an aberration quantity (namely, quantity-of-aberration) estimating method, and an aberration eliminating filter for eliminating the aberration. Furthermore, the present invention relates to a semiconductor manufacturing method for manufacturing a semiconductor device by transferring a circuit pattern while eliminating the aberration.
2. Description of the Related Art
Projection aligners for projecting a circuit pattern of a semiconductor device, which is formed on a mask, onto a wafer are required to have high resolution so as to achieve the transferring of a micro or fine pattern thereon. Generally, in proportion as the numerical aperture (NA) of a projection lens (or projecting lens) increases, or in proportion as the wavelength of exposure light decreases, the resolution is improved. The method of increasing the NA of the projection lens, however, causes a reduction in the focal depth (namely, the depth of focus) thereof at the time of transferring the pattern. Thus, there is a limit to the improvement of the resolution. On the other hand, the use of exposure light having short wavelength requires an extensive modification of the transferring process. The method of decreasing the wavelength of exposure light is, therefore, unpractical.
Thus, in Japanese Patent Laid-Open Nos. 4-251914 and 4-179213, there have been proposed projection aligners, by each of which the resolution can be enhanced by increasing the NA but, simultaneously, the focal depth can be enlarged, by the applicant of the present application. As illustrated in FIG. 19, in this projection aligner, a fly-eye lens 3 is placed diagonally to the front of a lamp house or lamp housing 1 by interposing a mirror 2 therebetween. Further, an aperture 4 is positioned in front of the fly-eye lens 3. Moreover, a blind 6 is placed in front of the aperture 4 by putting a condensing lens or condenser lens 5 therebetween. Furthermore, a photomask 10, on which a desired circuit pattern is formed, is disposed diagonally to the front of the blind 6 by interposing a condensing lens 7, a mirror 8 and a condensing lens 9 therebetween. In addition, a wafer 12 is placed in front of the photomask 10 by interposing a projection optical system or projecting lens system 11 therebetween. The contrast of an image at the time of defocusing is improved by putting a phase shift member, which is operative to cause a phase difference between light passing through the central portion of a transmitting zone or area and light passing though the peripheral area thereof, onto the pupillary surface or pupil plane of the projection optical system 11. Consequently, the focal depth is increased effectively.
However, in the case of the aforementioned conventional projection aligner, the aberration of the optical system is not taken into consideration. Generally, actual or practical optical systems have various aberrations. Typical aberrations are a spherical aberration, an astigmatism aberration, a field curvature and a coma aberration. It is known that theses aberrations can be expressed, as illustrated in FIGS. 20A to 20E, by being converted into wavefront aberrations, respectively. In these figures, .phi. denotes a shift quantity or distance of a wavefront; .rho. a radius on a pupillary surface (namely, .eta..xi.E -plane); .theta. an angle of rotation with respect to the axis .eta.; y.sub.0 coordinates on a wafer surface; and B to F constants. The details of these aberrations are described in various literatures, for example, "Principle of Optics I to III" (published by Tokai University Press.).
Because the optical systems of the conventional projection aligners have such aberrations, the conventional projection aligners have the problems that the image quality thereof is degraded and that the accuracy of transferring a circuit pattern is deteriorated.
The present invention is accomplished to solve such problems of the conventional projection aligners.